The present invention relates to a photogalvanic device, i.e. a device for the conversion of light to electrical energy.
U.S. Pat. No. 3,255,044 teaches a radiation cell for the conversion of high energy radiation, such as .alpha.,.beta. or .gamma. rays or ultraviolet radiation, into electrical energy. In the cell, the high energy radiation decomposes water with the production of gaseous hydrogen. The gaseous hydrogen formed by this decomposition passes into a gas space within the device and reacts at a catalyzed electrode, positioned at the interface between the gas phase and the liquid electrolyte, to form hydrogen ions with the release of electrons. These electrons pass from the electrode through an external circuit to the cathode of the device where a redox couple, present in the liquid electrolyte, is reduced (e.g. ferric iron present in the solution is reduced to ferrous iron). The cathode immersed in the electrolyte has a high over-voltage for the oxidation of hydrogen to hydrogen ion.
Such a device has numerous disadvantages. First, because of the requirement that water be decomposed with the formation of gaseous hydrogen, the device is sensitive only to radiation energetically sufficient to effect this decomposition. The device cannot, for instance, convert visible light to electrical energy since visible light is of insufficient energy to liberate gaseous hydrogen from water to any significant degree. Further, the device must include a gas-tight vessel in which both a liquid electrolyte phase and a gaseous hydrogen phase are present. Because of the requirements for a gas space and for the anode to be at the liquid-gas interface, severe restrictions are placed on the design of the cell. Further, the anode must be catalytically active towards hydrogen so that a low overvoltage for the oxidation of hydrogen to hydrogen ion is achieved.
The photoreducibility of certain dyes, e.g. thiazine dyes such as thionine (Lauth's violet), is known in the art. For example, E. Rabinowitch has studied the generation of an electric potential by a solution of thionine dye [J. Chem. Phys. 8, 551 (1940); Ibid 8, 560 (1940)] in a cell having one illuminated and one non-illuminated, or dark, electrode. Such cells are also discussed in Technical Documentary Report No ASD-TDR-62-373 published in May 1962 by the Flight Accessories Laboratory, Aeronautical Systems Division, Air Force Systems Command, Wright-Patterson Air Force Base, Ohio. These cells are not practical photogalvanic devices because of the difficulty encountered in constructing such cells wherein one electrode must be illuminated while the other electrode must remain dark.